1. Technical Field of the Invention
This invention relates to a magnetic sensor that has a magnetic movable to move responsive to a movement of an object-being-detected so that a movement of an object-being-detected, particularly a direction of movement thereof, can be detected by using a change of magnetic field due to the movement of the magnetic movable.
2. Description of the Related Art
Conventionally, there is well-known a magnetic sensor adapted to detect a moving direction of an object-being-detected by moving a magnetic movable having convexes in responsive to a movement of the object-being-detected and thereby detecting a change of magnetic field caused by the movement of the magnetic movable through the use of a magneto-resistance element (hereinafter referred to as an MR element).
Such existing magnetic sensors include, say, those having a structure that three MR elements are arranged opposite to a magnetic movable through a slight gap. The MR elements are arranged in a direction of movement of the magnetic movable by inserting those MR elements respectively in two bridge circuits at predetermined sides thereof. The magnetic movable, when moved, causes a resistance change in the MR elements, which is taken as voltage change on two systems from the bridge circuits. From the state of voltage change, detected is a moving direction of the magnetic movable and hence of the object-being-detected. (see JP-A-2002-90181, FIGS. 4-6, description page 6, for example).
In the existing magnetic sensor shown in JP-A-2002-90181, the two-system voltage changes taken out of the bridge circuits are converted by first and second comparator circuits into rectangular-wave signals. One of the rectangular-wave signals is inputted to a base terminal of an output transistor and to a D-terminal of a D-flip-flop circuit. The other rectangular-wave signal is inputted to a CL terminal of the D-flip-flop circuit. The D-flip-flop circuit has an output that is inputted to a base terminal of another transistor. This transistor has a collector terminal whose voltage is pulled up to the power voltage VCC, and an emitter terminal connected to an emitter terminal of the output transistor and grounded through a resistance.
The output transistor has an output signal that is delivered to a computer unit and then pulled up to the power voltage VCC. The output signal of the output transistor is inputted to third and fourth comparator circuits where compared with comparison levels 1 and 2, to obtain two output signals based on the comparison results. In the case one output signal is in a low state in level, a forward movement is to be recognized as to the magnetic movable. When the output signal is a rectangular wave, a reverse movement is to be recognized as to the magnetic movable.
However, in the existing magnetic sensor shown in JP-A-2002-90181, one rise edge of a rectangular-wave signal is used to recognize a moving direction of the magnetic movable. Thus, there problematically encounters a delay in the timing of detecting a moving direction of the magnetic movable.